In a mobile IT device such as a digital camera, a camera module is embedded therein for making a video or capturing a picture. In such a camera module, a VCM is provided as a means for moving the lens in order to make a focus on the object.
As illustrated in FIG. 1, a VCM actuator 12 coupled to the side surface of the lens 11 is located in the upper side of a bobbin support 14 of the housing 13.
The VCM actuator 12 comprises a permanent magnet 12B and a bobbin 12A.
The power supply of the camera becomes off when the mode is converted from the operating mode to the camera stop mode in the camera module 10 having the above described structure.
In this case, the bobbin 12A moves the lens 11 to the bottom surface 16 due to the force of a spring 19. In this way, when the lens 11 is moved to the bottom surface 16 noise is generated caused by the collision between the lower portion 12C of the bobbin 12A and the bobbin support 14 of the housing 13. Such noise is called allophone of a VCM.
A technique is also introduced in that in order to suppress such noise, the current applied to the VCM is not off when the mode is switched from the operating mode to the camera stop mode, but rather linearly reduced, the noise generated by the collision between the lower portion 12C of the bobbin 12A and the bobbin support 14 of the housing 13 is minimized thereby. However, although such technique is a method which can minimize the VCM noise, it is disadvantageous in that more time is required for the lens to be moved to the bottom surface since the applied current to the VCM is linearly reduced.
Also, a linearly increasing current is applied to the VCM in the initial stage for moving the lens as illustrated in FIG. 2, and the noise is generated by the deformation of the spring when the lens starts to move or start to stop due to the initial driving current, the elastic coefficient of spring, a stop friction, and the like. Thus, there is a necessity for removing or minimizing the noise caused by the current applied to VCM in the initial stage of driving the lens.
For reference, FIG. 2 illustrates the current applied to the VCM for initial driving of the lens and the displacement of the lens, and FIG. 3 illustrates the current applied to the VCM for returning the lens to the landing area and the displacement of the lens. Especially in FIG. 3, the displacement of the lens is separately presented according to the pose of the camera module, that is, face up, horizontal, and face down. Referring to FIG. 3, it can be seen that the lens is returning to the landing area at different current values depending on the position of the camera module. In addition, since the ‘start current’ in FIG. 2 is a current applied to the VCM when the lens starts to start, hereinafter in the following description, it will be referred to as ‘start current’ that is applied to the VCM at the time when the lens starts to move.